Previously, installed electrical wiring at a wellhead was spliced together with a metallic-screwed connector that held the spliced power cables together. The connector required a sleeve fitted over the cable to insulate the high voltage and amperage power cable which could be easily installed under all working conditions. Prior sleeves were fabricated from neoprene rubber, providing the necessary electrical insulation preventing contact with the exterior cover. As long as the weather stayed warm, this previous arrangement was adequate. However, in any extreme temperature or temperature changes in a short time period, the neoprene sleeve would become brittle and difficult to handle. Installation was then problematic; any bending or movement of the wiring within the sleeve caused cracking of the neoprene sleeve and loss of its insulating efficiency. The present invention comprises an insulating sleeve that allows for rigidity, efficient installation or reinstallation in all weather, superior insulating qualities in high voltage/amperage installations, and resists cracking or leakage as it ages. An additional cap on the sleeve makes the entire boot assembly water-resistant.